1. Field of the Invention
This invention relates to an apparatus and method for performing medical bacteriology and clinical chemistry by means of changes in turbidity, color or other optical properties which serve as indicators of biological activity, content or condition of the specimen under investigation. More particularly, this invention relates to an apparatus for automatically and continuously determining the rate of the bacterial growth by photometric means.
The specimen may be a biological fluid recovered from a patient, such as serum, plasma, urine, cerebrospinal fluid, acities or an artificially prepared nutrient or reagent fluid capable of supporting or demonstrating phenomena correlative to pathological, physiological, chemical, or metabolic state, activity or content.
Current clinical practice in medical microbiology and bacteriology is largely concerned with the isolation and evaluation of pathogenic bacteria from specimens of clinical interest. Such specimens may be derivative of both the patient, for example his blood, urine, wound exudate, or other biological fluid, or his immediate or etiological environment, such as food, air, water, or other factors of an infection or communicable disease vector system. Concomitant with the identification of a viral, mycotic, or bacterial pathogen agent in a specimen is the requirement for determining what antibiotic agent is effective against a specific pathogen and to what degree it is effective in comparison to other chemotherapeutic agents available to the clinician as treatment of the condition.
Assay of biological fluids for levels of antibiotic, in vivo, also falls within the scope of medical microbiology, although the performance of the procedure is far less frequent than the above-described identifications of antibiotic effectiveness or sensitivity, a term derived from the subject organism's "sensitivity" to a drug. The assay procedure is extremely difficult to perform under presently available conditions in the laboratory and as such it is used only in research or in cases of extreme clinical importance. Although the information derived from such a procedure is very valuable to the clinician, it is an abnormally severe imposition on the laboratory staff.
The determination of minimum inhibitory concentration (MIC) of the antibiotic effectiveness against a particular pathogen also falls within the scope of medical microbiology, although not performed as often as antibiotic sensitivity.
2. Description of the Prior Art THE PRIOR ART
Prior art identification procedures in the bacteriology laboratory are based on the taxonomic evaluation of cultures grown on solid or gelled media, immunofluorescent microscopic evaluation or color change of a nutrient media such that bacterial growth is indicated by reaction with metabolic products derived from such growth. Nutrient media can also be formulated to support the growth of specific pathogens or classes of pathogens to the exclusion of others and to indicate such growth by color change.
Recently there have been a number of attempts for meeting the need for automating the tedious manual methods for the determination of an organism's sensitivity. Although there are a number of automatic devices on the market, they have not efficiently solved the problems of cross-contamination between samples and the slow rate of analysis and they have not provided for a convenient means of random sample ingress and egress during the bacterial growth cycle. Because of their complexity, prior art automatic devices, require a great deal of maintenance and laboratory space.
Examples of such complex prior art devices which photometrically analyze specimens in a plurality of cuvettes are disclosed in several recent patents including Wood et al, U.S. Pat. No. 3,523,737 and Kuzel et al, U.S. Pat. No. 3,609,040. These devices contain a plurality of moving parts which require constant maintenance and decrease their reliability. There is a long-felt need for an apparatus utilizing photometric principles which is simplistic in design with almost no moving parts and with all operations carried out pneumatically and optoelectronically.
In an entirely different application, i.e. the textile dyeing industry, than that of the present invention, a colorimeter has been described in Ward, U.S. Pat. No. 3,531,208, in which a plurality of dye samples are optically measured by means of a plurality of detectors and a plurality of amplifiers and the measurement is compared against a standard color chart. This reference is recited herein to show the general state of the colorimetric art.